Image processing apparatus, image processing method, and non-transitory computer-readable storage medium

ABSTRACT

A detection sensitivity is set such that a detection sensitivity for a defect corresponding to a predetermined local pattern in a reference image, which is a reference printing result, is lower than for a region other than the predetermined local pattern in the reference image. Image data representing an image of an inspection target is acquired and the image of the inspection target is inspected based on the reference image and the set detection sensitivity.

BACKGROUND OF THE INVENTION Field of the Invention

The present invention relates to an image processing technique forinspecting a print product.

Description of the Related Art

In a print product output from a printing apparatus, a color materialsuch as ink or toner may be attached to an unintended portion and maycause stain. Or a sufficient color material may not be attached to aportion where an image should be formed., and color loss may occur,where the color is lighter than normal. Such a defect, such as stain orcolor loss, in the print product decreases the quality of the printproduct. Thus, the quality of the print product needs to be guaranteedby inspecting the presence or absence of a defect in the print product.A visual inspection for visually inspecting the presence or absence of adefect in the print product requires a significant cost. Thus, aninspection system that performs an automatic inspection is developed. Insuch an inspection system, it is possible to determine the presence orabsence of a defect based on the difference between a reference imageregistered in advance and serving as an inspection standard for a printproduct and an inspection target image obtained by scanning a printproduct and serving as an inspection target. Japanese Patent Laid-OpenNo. 2018-155736 discusses a technique for correcting an inspectionthreshold to relax the inspection threshold in a region near an edgeextracted from a reference image and inspecting a print product based onthe difference between the reference image and an inspection targetimage and the corrected inspection threshold.

In the technique discussed in the publication of Japanese PatentLaid-Open No. 2018-155736, however, a defect present in the vicinity ofa region including a feature such as an edge was undetectable in theinspection target image.

SUMMARY OF THE INVENTION

The present disclosure is directed to providing a process for improvingthe accuracy of inspection of the vicinity of a region including afeature in an inspection target image.

According to the first aspect of the present invention, there isprovided an image processing apparatus comprising: a first setting unitconfigured to set a detection sensitivity such that the detectionsensitivity for a defect corresponding to a predetermined local patternin a reference image, which is a reference printing result, is lowerthan for a region other than the predetermined local pattern in thereference image; an acquisition unit configured to acquire image datarepresenting an image of an inspection target; and a processing unitconfigured to inspect the image of the inspection target based on thereference image and the set detection sensitivity.

According to the second aspect of the present invention, there isprovided an image processing method comprising: setting a detectionsensitivity such that the detection sensitivity for a defectcorresponding to a predetermined local pattern in a reference image,which is a reference printing result, is lower than for a region otherthan the predetermined local pattern in the reference image; acquiringimage data representing an image of an inspection target; and inspectingthe image of the inspection target based on the reference image and theset detection sensitivity.

According to the third aspect of the present invention, there isprovided a non-transitory computer-readable storage medium storinginstructions that, when executed by a computer, cause the computer toperform a method comprising: setting a detection sensitivity such thatthe detection sensitivity for a defect corresponding to a predeterminedlocal pattern in a reference image, which is a reference printingresult, is lower than for a region other than the predetermined localpattern in the reference image; acquiring image data representing animage of an inspection target; and inspecting the image of theinspection target based on the reference image and the set detectionsensitivity.

Further features of the present invention will become apparent from thefollowing description of exemplary embodiments with reference to theattached drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a diagram illustrating a configuration of a printing systemincluding an image processing apparatus.

FIG. 2 is a block diagram illustrating a functional configuration of theimage processing apparatus.

FIG. 3 is a flowchart illustrating processing executed by the imageprocessing apparatus.

FIGS. 4A and 4B are diagrams illustrating examples of a reference imageand an inspection target image.

FIG. 5 is a diagram illustrating examples of inspection regions.

FIG. 6 is a diagram illustrating examples of detection sensitivities.

FIG. 7 is a flowchart illustrating a process of extracting a localpattern region.

FIGS. 8A, 8B, 8C, and 8D are diagrams illustrating examples of localpattern regions.

FIG. 9 is a flowchart illustrating a process of adjusting the detectionsensitivities.

FIGS. 10A and 10B are diagrams illustrating examples of the adjusteddetection sensitivities.

FIG. 11 is a flowchart illustrating an inspection process.

FIG. 12 is a diagram illustrating an overview of the inspection process.

FIG. 13 is a flowchart illustrating a process of extracting localpattern regions.

FIGS. 14A and 14B are diagrams illustrating examples of local patternregions.

FIG. 15 is a flowchart illustrating a process of adjusting detectionsensitivities.

FIGS. 16A and 16B are diagrams illustrating examples of the adjusteddetection sensitivities.

DESCRIPTION OF THE EMBODIMENTS

The present exemplary embodiments will be described below with referenceto the drawings. The following exemplary embodiments do not necessarilylimit the present invention. Not all the combinations of the featuresdescribed in the present exemplary embodiments are essential for amethod for solving the issues in the present invention. Each of theembodiments of the present invention described below can be implementedsolely or as a combination of a plurality of the embodiments or featuresthereof where necessary or where the combination of elements or featuresfrom individual embodiments in a single embodiment is beneficial.

First Exemplary Embodiment

in a first exemplary embodiment, a region corresponding to a localpattern is extracted from a reference image, and an inspection processis performed by lowering a detection sensitivity for a defect similar tothe local pattern. The inspection according to the present exemplaryembodiment is performed based on the absolute value of the differencebetween an image (a reference image) representing a targeted printingresult and an image (an inspection target image) which is an inspectiontarget,

<Configuration of Printing System>

FIG. 1 is a diagram illustrating an example of the configuration of anentire printing system including an image processing apparatus 100 andthat outputs and inspects a print product. The printing system accordingto the present exemplary embodiment includes the image processingapparatus 100, a print server 180, and a printing apparatus 190. Theprint server 180 generates a print job of a document to be printed andinputs the print job to the printing apparatus 190. The printingapparatus 190 forms an image on a recording medium (a print sheet) basedon the print job input from the print server 180. The printing apparatus190 includes a sheet feeding unit 191, and a user sets the print sheetin advance in the sheet feeding unit 191. When the print job is input,the printing apparatus 190 conveys the print sheet set in the sheetfeeding unit 191 along a conveying path 192 while forming an image onthe surface (one side or both sides) of the print sheet and sends theprint sheet to the image processing apparatus 100. The printingapparatus 190 according to the present exemplary embodiment is aprinting apparatus using an electrophotographic method, but may be aprinting apparatus using an offset printing method or an inkjet method.

The image processing apparatus 100 inspects a defect on a print productas an inspection target on which printing is performed. The printproduct as the inspection target, which is obtained by the printingapparatus 190 forming the image on the print sheet, is conveyed alongthe conveying path 192 and inspected by the image processing apparatus100. The image processing apparatus 100 functions as an inspectionprocessing apparatus. The image processing apparatus 100 includes acentral processing unit (CPU) 101, a random-access memory (RAM) 102, anda read-only memory (ROM) 103. The image processing apparatus 100 alsoincludes a storage device 104, an image reading device 105, a printinginterface (I/F) 106, a general-purpose I/F 107, a user interface (UI)panel 108, and a main bus 109. Further, the image processing apparatus100 includes a conveying path 110 for the print product and connected.to the conveying path 192 of the printing apparatus 190, an output tray111 for a final print product having passed the inspection, and anoutput tray 112 for a print product having failed the inspection becauseof a defect found. A configuration may be employed in which the printproduct is not classified into only two types, namely pass and fail, butis classified into finer categories. In the printing system, the storagedevice 104, the image reading device 105, the UI panel 108, theconveying path 110, the output tray 111, and the output tray 112 may beprovided outside the image processing apparatus 100.

The CPU 101 is a processor that performs overall control of thecomponents of the image processing apparatus 100. The RAM 102 functionsas a main memory and a work area for the CPU 101. The ROM 103 stores agroup of programs to be executed by the CPU 101. The storage device 104stores an application to be executed by the CPU 101 and data to be usedin image processing. The image reading device 105 is a scanner. Theimage reading device 105 reads one side or both sides of the printproduct sent from the printing apparatus 190 on the conveying path 110and acquires image data.

The printing I/F 106 is an interface connected to the printing apparatus190 and is for synchronizing the processing timings of the print productbetween the image processing apparatus 100 and the printing apparatus190 and notifying the image processing apparatus 100 and the printingapparatus 190 of the operation states of each other. The general-purposeI/F 107 is a serial bus interface such as a Universal Serial Bus (USB)interface and an institute of Electrical and Electronics Engineers(IEEE) 1394 interface and enables the user to carry data of a log. TheUI panel 108 is a display device such as a liquid crystal display andfunctions as a user interface for notifying the user of the currentstate and settings of the image processing apparatus 100. The UI panel108 can include an input device such as a touch panel or a button andmay receive an instruction from the user regarding the inspection. Theinput device may be provided separately from the UI panel 108, as in amouse or a keyboard. The main bus 109 is a transmission path to whichthe modules of the image processing apparatus 100 are connected.

The image processing apparatus 100 conveys the print product sent fromthe printing apparatus 190 on the conveying path 110 while, based on theimage data of the print product read by the image reading device 105,performing an inspection process described below. If the print productpasses the inspection, the print product is conveyed to the output tray111 for pass. If the print product fails the inspection, the printproduct is conveyed to the output tray 112 for fail. Consequently, onlyprint products confirmed as satisfying a quality standard can becollected in the output tray 111 as print products to be delivered.

<Functional Configuration of image Processing Apparatus>

FIG. 2 illustrates the functional configuration of the image processingapparatus 100. The image processing apparatus 100 includes a referenceimage setting unit 201, a region setting unit 202, a detectionsensitivity setting unit 203, a local pattern extraction unit 204, adetection sensitivity adjustment unit 205, an image acquisition unit206, and an inspection processing unit 207.

The reference image setting unit 201 sets an image represented by imagedata recorded in the RAM 102 or the storage device 104 as a referenceimage. Based on an instruction from the user acquired via the UI panel108, the region setting unit 202 sets inspection regions in thereference image. Based on an instruction from the user acquired via theUI panel 108, the detection sensitivity setting unit 203 sets detectionsensitivities for defects in each of the inspection regions. Thedetection sensitivities according to the present exemplary embodimentare set for the respective types of defects. The types of defectsaccording to the present exemplary embodiment are two types, namely apoint-like defect and a line-like defect. The local pattern extractionunit 204 extracts a region corresponding to a particular local patternfrom the reference image. The local pattern which is the extractiontarget according to the present exemplary embodiment is a line-likepattern, and the local pattern extraction unit 204 extracts a regioncorresponding to a line-like pattern from the reference image. Thedetection sensitivity adjustment unit 205 lowers the detectionsensitivity for a defect similar to the local pattern in a regioncorresponding to the local pattern. The detection sensitivity adjustmentunit 205 according to the present exemplary embodiment lowers thedetection sensitivity for a line-like defect in the region correspondingto the line-like pattern. The image acquisition unit 206 acquiresinspection target image data representing an inspection target image andobtained by the image reading device 105 reading a print product on theconveying path 110. The acquired inspection target image data is held inthe RAM 102 or the storage device 104. The inspection processing unit207 performs an inspection process on the inspection target image basedon the difference between the reference image and the inspection targetimage and the detection sensitivities, and outputs the inspectionresult.

<Processing Executed by Image Processing Apparatus>

FIG. 3 is a flowchart illustrating processing executed by the imageprocessing apparatus 100. In step 5301, the reference image setting unit201 sets a reference image. FIG. 4A illustrates an example of thereference image. Reference image data representing the reference imageis created in advance based on a scanned image obtained by reading aprint product output from the printing apparatus 190 and is recorded inthe RAM 102 or the storage device 104.

In step S302, the region setting unit 202 sets inspection regions in thereference image based on an instruction from the user acquired throughthe UI panel 108. FIG. 5 illustrates an example of the inspectionregions. The region setting unit 202 according to the present exemplaryembodiment sets inspection regions A and B in the reference image. Instep S303, the detection sensitivity setting unit 203 sets detectionsensitivities for defects in each of the inspection regions based on aninstruction from the user acquired via the UI panel 108. The detectionsensitivity setting unit 203 according to the present exemplaryembodiment sets detection sensitivities for a point-like defect and aline-like defect in each of the inspection regions at three levels,namely high, medium, and low. The higher the detection sensitivity is,the lower the contrast between a defect and the background is, or thesmaller the size of a defect is. FIG. 6 illustrates examples of thedetection sensitivities. In the inspection region A, the detectionsensitivities for a point-like defect and a line-like defect are set tohigh. In the inspection region B, the detection sensitivities for apoint-like defect and a line-like defect are set to medium.

In step S304, the local pattern extraction unit 204 extracts a regioncorresponding to a local pattern in the reference image. FIG. 7 is aflowchart illustrating the process of extracting the regioncorresponding to the local pattern. The details of the process ofextracting the region corresponding to the local pattern are describedbelow. In step S701, the local pattern extraction unit 204 applies aline enhancement filter to the reference image, thereby enhancing aline-like pattern included in the reference image. As a result of usingthe line enhancement filter, the more the pixel corresponds to theline-like pattern, the greater the pixel value of the pixel is.Hereinafter, an image obtained by applying the line enhancement filterto the reference image will be referred to as a “line-enhanced image”.The line enhancement filter according to the present exemplaryembodiment is a known Sobel filter. Alternatively, a knowntwo-dimensional filter such as a Prewitt filter may be used. In stepS702, the local pattern extraction unit 204 extracts a regioncorresponding to the line-like pattern in the line-enhanced image. Inthe present exemplary embodiment, an edge region is extracted as theregion corresponding to the line-like pattern. FIG. 8A illustrates anexample of the edge region. Specifically, the local pattern extractionunit 204 performs a threshold process on pixels in the line-enhancedimage and extracts a pixel having a pixel value greater than athreshold, as an edge pixel included in the edge region. A knownmorphological process may be applied to the extracted edge region,thereby correcting the edge region.

In step S305, the detection sensitivity adjustment unit 205 lowers thedetection sensitivity for a defect similar to the local pattern in theregion corresponding to the local pattern. FIG. 9 is a flowchartillustrating the process of adjusting the detection sensitivities. Thedetails of the process of adjusting the detection sensitivities aredescribed below. In step S901, the detection sensitivity adjustment unit205 divides each of the inspection regions based on the edge region.FIG. 8B illustrates examples of the divided inspection regions. In thepresent exemplary embodiment, the detection sensitivity adjustment unit205 sets an edge region in the inspection region A as a region Ae andsets a non-edge region in the inspection region A as a region An. Thedetection sensitivity adjustment unit 205 sets an edge region in theinspection region B as a region Be and sets a non-edge region in theinspection region B as a region Bn. In step S902, the detectionsensitivity adjustment unit 205 lowers the detection sensitivity for aline-like defect as a defect similar to the line-like pattern in theedge region. Specifically, in the region Ae, the detection sensitivityadjustment unit 205 sets the detection sensitivity for a line-likedefect to be lower than the detection sensitivity set for the inspectionregion A and sets the detection sensitivity for a point-like defect tobe the same as the detection sensitivity set for the inspection regionA. In the region Be, the detection sensitivity adjustment unit 205 setsthe detection sensitivity for a line-like defect to be lower than thedetection sensitivity set for the inspection region B and sets thedetection sensitivity for a point-like defect to be the same as thedetection sensitivity set for the inspection region B. A detectionsensitivity for the region An is set to be the same as the detectionsensitivity set for the inspection region A, and a detection sensitivityfor the region Bn is set to be the same as the detection sensitivity setfor the inspection region B. FIG. 10A illustrates examples of theadjusted detection sensitivities.

In step S306, the image acquisition unit 206 acquires inspection targetimage data representing an inspection target image. FIG. 4B illustratesan example of the inspection target image. In step S307, the inspectionprocessing unit 207 performs an inspection process on the inspectiontarget image based on the difference between the reference image and theinspection target image and the detection sensitivities, and outputs theinspection result. The details of the inspection process will bedescribed below. In step S308, the inspection processing unit 207determines whether the processing is to be ended based on printinformation from the printing apparatus 190 or an instruction from theuser acquired through the UI panel 108. If it is determined that theprocessing is not to be ended (NO in step S308), the processing returnsto step S306.

<Inspection Process>

FIG. 11 is a flowchart illustrating the inspection process. FIG. 12 is adiagram illustrating an overview of the inspection process. The detailsof the inspection process are described below. In step S1101, based onthe reference image and the inspection target image, the inspectionprocessing unit 207 calculates the absolute value of the difference inluminance value between corresponding pixels in the reference image andthe inspection target image and generates a difference image having theabsolute value of the difference in luminance value at each pixel. Instep S1102, the inspection processing unit 207 enhances a defect in aprocessing target included in the difference image, thereby generating adefect-enhanced image. In a case where the defect as the processingtarget is a line-like defect, a line enhancement filter is applied tothe difference image. As the line enhancement filter, a Sobel filter isused. In a case where the defect as the processing target is apoint-like defect, a point enhancement filter is applied to thedifference image. As the point enhancement filter, a knowntwo-dimensional Laplacian-of-Gaussian (Lot filter is used.Alternatively, as the point enhancement filter, a known two-dimensionalfilter such as a Difference-of-Gaussian (DoG) filter may be used.

In step S1103, the inspection processing unit 207 sets thresholds to beused in the inspection based on the detection sensitivitiescorresponding to an inspection region as a processing target and thedefect as the processing target, In the present exemplary embodiment,the inspection processing unit 207 compares pixel values in thedefect-enhanced image with a threshold Th₁, thereby detecting defectpixels included in a defect region. Further, to determine whether thedefect region has a sufficient area, the inspection processing unit 207compares the area of the defect region composed of the group of defectpixels linked together with a threshold Th₂. In step S1103, theinspection processing unit 207 sets the thresholds Th₁ and Th₂.Specifically, the inspection processing unit 207 sets each threshold sothat the higher the detection sensitivity is, the lower the contrastbetween a defect and the background can be, or the smaller the size of adefect can be. The inspection processing unit 207 sets the threshold Th₁so that the higher the detection sensitivity is, the smaller the valueof the threshold Th₁ is. The inspection processing unit 207 sets thethreshold Th₂ so that the higher the detection sensitivity is, thesmaller the value of the threshold Th₂ is. For example, in the presentexemplary embodiment, since the detection sensitivity for a line-likedefect is higher in the region An than in the region Ae, the thresholdTh₁ is set to be smaller in the region An than in the region Ac, and thethreshold Th₂ is set to be smaller in the region An than in the regionAe.

In step S1104, the inspection processing unit 207 performs a thresholdprocess on pixel values in the defect-enhanced image using the thresholdTh₁. The inspection processing unit 207 detects, among pixels in thedefect-enhanced image, a pixel having a pixel value greater than orequal to the threshold Th₁, as a defect pixel by the threshold process.In step S1105, the inspection processing unit 207 performs a thresholdprocess on the areas of defect regions in the defect-enhanced imageusing the threshold Th₂. The inspection processing unit 207 removes,from the defect pixels detected in step S1104, pixels in a defect regionwhere the number of linked pixels is smaller than the threshold Th₂ bythe threshold process.

In step S1106, the inspection processing unit 207 identifies a regioncommon to the inspection region as the processing target and the defectregions. By this, it is possible to detect only the defect regions inthe inspection region as the processing target. In step S1107, theinspection processing unit 207 determines whether there is an inspectionregion that has not yet been processed. If there is an inspection regionthat has not yet been processed (YES in step S1107), the inspectionregion as the processing target is updated, and the processing returnsto step S1103. If there is not an inspection region that has not yetbeen processed (NO in step S1107), the processing proceeds to stepS1108.

In step S1108, the inspection processing unit 207 integrates the defectregions in each of the inspection regions. This can acquire a defectregion corresponding to the defect as the processing target. In stepS1109, the inspection processing unit 207 determines whether there is adefect type that has not yet been processed. If there is a defect typethat has not yet been processed (YES in step S1109), the defect as theprocessing target is updated, and the processing returns to step S1102.If there is not a defect type that has not yet been processed (NO instep S1109), the processing proceeds to step S1110. In step S1110, theinspection processing unit 207 outputs the inspection result. If thereis not a defect region with respect to all the defect types, theinspection result is pass. If there is a defect region with respect toany of the defect types, the inspection result is fail.

Effects of First Exemplary Embodiment

As described above, the image processing apparatus 100 according to thepresent exemplary embodiment sets a reference image as a targetedprinting result. The image processing apparatus 100 sets detectionsensitivities for a plurality of types of defects. The image processingapparatus 100 extracts a region corresponding to a local pattern fromthe reference image. The image processing apparatus 100 adjusts thedetection sensitivities to lower the detection sensitivity for a defectsimilar to the local pattern in the region corresponding to the localpattern. The image processing apparatus 100 acquires image datarepresenting an image as an inspection target. Based on the referenceimage and the adjusted detection sensitivities, the image processingapparatus 100 inspects the image as the inspection target. This canimprove the accuracy of inspection of the vicinity of a region includinga feature in an inspection target image.

<Variations>

The region setting unit 202 according to the present exemplaryembodiment sets two regions, namely the inspection regions A and B, asthe inspection regions. The method for setting the inspection regions,however, is not limited to this. Alternatively, for example, the entirereference image may be set as a single inspection region. Yetalternatively, three or more regions may be set as the inspectionregions. Yet alternatively, a non-inspection region where a defect isnot to be detected may be set. In a case where the non-inspection regionis set, pixel values in the non-inspection region are set to 0 in thedifference image generated in step S1101, whereby it is possible toavoid detecting a defect in the non-inspection region.

The detection sensitivity setting unit 203 according to the presentexemplary embodiment sets the detection sensitivities at three levels.The method for setting the detection sensitivities, however, is notlimited to this. Alternatively, for example, the detection sensitivitiesmay be set at two levels, or may be set at four or more levels. Yetalternatively, the detection sensitivity for any of the defects may befixed.

The local pattern extraction unit 204 according to the present exemplaryembodiment extracts the region corresponding to the line-like pattern asthe region corresponding to the local pattern, but may extract a regioncorresponding to a point-like pattern. In this case, in step S701, thelocal pattern extraction unit 204 applies a point enhancement filter tothe reference image, thereby enhancing a point-like pattern included inthe reference image. By the point enhancement filter, the more the pixelcorresponds to the point-like pattern, the greater the pixel value ofthe pixel is. Hereinafter, an image obtained by applying the pointenhancement filter to the reference image will be referred to as a“point-enhanced image”. As the point enhancement filter, atwo-dimensional LoG filter is used. In step S702, the local patternextraction unit 204 extracts a region corresponding to the point-likepattern in the point-enhanced image. As the region corresponding to thepoint-like pattern, a dot region is extracted. FIG. 8C illustrates anexample of the dot region. Specifically, the local pattern extractionunit 204 performs a threshold process on pixels in the point-enhancedimage and extracts a pixel having a pixel value greater than athreshold, as a dot pixel included in the dot region. A knownmorphological process may be applied to the extracted dot region,thereby correcting the dot region.

In step S901, the detection sensitivity adjustment unit 205 divides eachof the inspection regions based on the dot region. FIG. 8D illustratesexamples of the divided inspection regions. The detection sensitivityadjustment unit 205 sets a dot region in the inspection region A as aregion Ad and sets a non-dot region in the inspection region A as aregion An. The detection sensitivity adjustment unit 205 sets a dotregion in the inspection region B as a region Bd and sets a non-dotregion in the inspection region B as a region Bn. In step S902, thedetection sensitivity adjustment unit 205 lowers the detectionsensitivity for a point-like defect as a defect similar to thepoint-like pattern in the dot region. Specifically, in the region Ad,the detection sensitivity adjustment unit 205 sets the detectionsensitivity for a point-like defect to be lower than the detectionsensitivity set for the inspection region A and sets the detectionsensitivity for a line-like defect to be the same as the detectionsensitivity set for the inspection region A. In the region Bd, thedetection sensitivity adjustment unit 205 sets the detection sensitivityfor a point-like defect to be lower than the detection sensitivity setfor the inspection region B and sets the detection sensitivity for aline-like defect to be the same as the detection sensitivity set for theinspection region B. A detection sensitivity for the region An is set tobe the same as the detection sensitivity set for the inspection regionA, and a detection sensitivity for the region Bn is set to be the sameas the detection sensitivity set for the inspection region B. FIG. 10Billustrates examples of the adjusted detection sensitivities.

The types of defects according to the present exemplary embodiment aretwo types, namely a point-like defect and a line-like defect.Alternatively, for example, line-like defects different in direction,such as a vertical line-like defect and a horizontal line-like defect,may be detected as different defect types, In a case where the defect asthe processing target is a vertical line-like defect, then in stepS1102, the inspection processing unit 207 applies a vertical lineenhancement filter for enhancing a line in a vertical direction to thedifference image. In a case where the defect as the processing target isa horizontal line-like defect, then in step S1102, the inspectionprocessing unit 207 applies a horizontal line enhancement filter forenhancing a line in a horizontal direction to the difference image.

In the inspection process according to the present exemplary embodiment,the threshold process on the pixel values and the threshold process onthe areas are performed. Alternatively, defect regions may be detectedby performing only the threshold process on the pixel values. In thiscase, as the thresholds corresponding to the detection sensitivities,only a threshold for the pixel values needs to be set.

In the present exemplary embodiment, the user is notified of whether theinspection target image passes or fails the inspection. Alternatively, adefect region in the inspection target image having failed theinspection may be displayed on the UI panel 108.

Second Exemplary Embodiment

In the first exemplary embodiment, a region corresponding to a line-likepattern is extracted as a region corresponding to a local pattern from areference image, and a detection sensitivity for a line-like defect islowered, in a second exemplary embodiment, a region corresponding toeach of a plurality of types of local patterns is extracted from areference image, and a detection sensitivity for a defect similar toeach of the local patterns is lowered. The configuration of a printingsystem and functional configuration of an image processing apparatus 100according to the present exemplary embodiment are equivalent to thoseaccording to the first exemplary embodiment, and therefore are notdescribed. The processes of steps S304 and S305, which are differentbetween the present exemplary embodiment and the first exemplaryembodiment, are mainly described below. Components similar to those ofthe first exemplary embodiment are designated by the same signs in thedescription.

<Process of Extracting Region Corresponding to Each of Local Patterns>

In step S304, the local pattern extraction unit 204 extracts a regioncorresponding to each of a plurality of types of local patterns in thereference image. In the present exemplary embodiment, a regioncorresponding to a line-like pattern and a region corresponding to apoint-like pattern are extracted as the plurality of types of localpatterns. FIG. 13 is a flowchart illustrating the process of extractingthe region corresponding to each of the plurality of types of localpatterns. The details of the process of extracting the regioncorresponding to each of the plurality of types of local patterns aredescribed below.

In step S1301, the local pattern extraction unit 204 enhances a localpattern as a processing target included in the reference image, in acase where the local pattern as the processing target is the line-likepattern, the local pattern extraction unit 204 applies a lineenhancement filter to the reference image. In a case where the localpattern as the processing target is the point-like pattern, the localpattern extraction unit 204 applies a point enhancement filter to thereference image. In step S1302, the local pattern extraction unit 204extracts the region corresponding to the local pattern in an image wherethe local pattern is enhanced, In a case where the local pattern as theprocessing target is the line-like pattern, the local pattern extractionunit 204 performs a threshold process on pixels in a line-enhanced imageand extracts a pixel having a pixel value greater than a threshold, asan edge pixel. In a case where the local pattern as the processingtarget is the point-like pattern, the local pattern extraction unit 204performs a threshold process on pixels in a point-enhanced image andextracts a pixel having a pixel value greater than a threshold, as a dotpixel.

In step S1303, the local pattern extraction unit 204 determines whetherthere is a local pattern that has not yet been processed. If there is alocal pattern that has not yet been processed (YES in step S1303), thelocal pattern as the processing target is updated, and the processingreturns to step S1301. If there is not a local pattern that has not yetbeen processed (NO in step S1303), the processing proceeds to stepS1304. In step S1304, the local pattern extraction unit 204 integratesthe regions corresponding to each of the plurality of types of localpatterns. Specifically, the local pattern extraction unit 204 replaces apixel included in both the edge region and the dot region with a pixelbelonging to either one of the regions. The local pattern extractionunit 204 according to the present exemplary embodiment replaces a pixelincluded in both the edge region and the dot region with an edge pixelincluded in the edge region. FIG. 14A illustrates examples of theregions corresponding to the local patterns extracted in the process ofstep S1304.

<Process of Adjusting Detection Sensitivities>

In step S305, the detection sensitivity adjustment unit 205 lowers thedetection sensitivity for a line-like defect in the edge region andlowers the detection sensitivity for a point-like defect in the dotregion. FIG. 15 is a flowchart illustrating the process of adjusting thedetection sensitivities. The details of the process of adjusting thedetection sensitivities are described below. In step S1501, thedetection sensitivity adjustment unit 205 divides each of the inspectionregions based on a region corresponding to a local pattern as aprocessing target. FIG. 14B illustrates examples of the dividedinspection regions. In the inspection region A, the detectionsensitivity adjustment unit 205 sets an edge region as a region Ac, setsa dot region as a region Ad, and sets another region as a region An. Inthe inspection region B, the detection sensitivity adjustment unit 205sets an edge region as a region Be, sets a dot region as a region Bd,and sets another region as a region Bn.

In step S1502, in the region corresponding to the local pattern as theprocessing target, the detection sensitivity adjustment unit 205 lowersthe detection sensitivity for a defect similar to the local pattern asthe processing target. In a case where the local pattern as theprocessing target is the line-like pattern, the detection sensitivityadjustment unit 205 lowers the detection sensitivity for a line-likedefect in the edge region. Specifically, in the region Ae, the detectionsensitivity adjustment unit 205 sets the detection sensitivity forline-like defect to be lower than the detection sensitivity set for theinspection region A. In the region Be, the detection sensitivityadjustment unit 205 sets the detection sensitivity for a line-likedefect to be lower than the detection sensitivity set for the inspectionregion B. In a case where the local pattern as the processing target isthe point-like pattern, the detection sensitivity adjustment unit 205lowers the detection sensitivity for a point-like defect in the dotregion. Specifically, in the region Ad, the detection sensitivityadjustment unit 205 sets the detection sensitivity for a point-likedefect to be lower than the detection sensitivity set for the inspectionregion A. In the region Bd, the detection sensitivity adjustment unit205 sets the detection sensitivity for a point-like defect to be lowerthan the detection sensitivity set for the inspection region B. FIG. 16Aillustrates examples of the adjusted detection sensitivities.

In step S1503, the detection sensitivity adjustment unit 205 determineswhether there is a local pattern that has not yet been processed. Ifthere is a local pattern that has not yet been processed (YES in stepS1503), the local pattern as the processing target is updated, and theprocessing returns to step S1502, if there is not a local pattern thathas not yet been processed (NO in step S1503), the process of step S305ends.

Effects of Second Exemplary Embodiment

As described above, the image processing apparatus 100 according to thepresent exemplary embodiment extracts a region corresponding to each ofa plurality of types of local patterns and adjusts detectionsensitivities according to the extracted region. This can improve theaccuracy of inspection of the vicinity of a region including a featurein an inspection target image.

<Variations>

In the present exemplary embodiment, as the regions corresponding to thelocal patterns, the edge region and the dot region are extracted. Thelocal patterns, however, are not limited to these regions. For example,local patterns of the same type but different in contrast with thebackground may be separately extracted. In this case, detectionsensitivities are adjusted so that the higher the contrast between theregion corresponding to the local pattern and the background is, thelower the detection sensitivity is. As an example, a case is describedwhere a high-contrast edge region and a low-contrast edge region areseparately extracted. First, a threshold Th_(EH) corresponding to thehigh-contrast edge region and a threshold Th_(EL) corresponding to thelow-contrast edge region are set. The value of the threshold Th_(EH) isgreater than that of the threshold Th_(EL).

In step S1302, in a case where the local pattern as the processingtarget is a high-contrast edge, the local pattern extraction unit 204performs a threshold process on pixels in a line-enhanced image andextracts a pixel having a pixel value greater than the thresholdTh_(EH), as a pixel in the high-contrast edge region. In a case wherethe local pattern as the processing target is a low-contrast edge, thelocal pattern extraction unit 204 performs a threshold process on pixelsin a line-enhanced image and extracts a pixel having a pixel valuegreater than the threshold Thu., as a pixel in the low-contrast edgeregion. In step S1304, the local pattern extraction unit 204 replaces,among the pixels in the low-contrast edge region, a pixel redundant witha pixel in the high-contrast edge region with a pixel in thehigh-contrast edge region.

In step S1501, in the inspection region A, the detection sensitivityadjustment unit 205 sets a high-contrast edge region as a region Ae_(H),sets a low-contrast edge region as a region Ae_(H), and sets anotherregion as a region An. In the inspection region B, the detectionsensitivity adjustment unit 205 sets a high-contrast edge region as aregion Be_(H), sets a low-contrast edge region as a region Be_(L), andsets another region as a region Bn. In step S1502, the detectionsensitivity adjustment unit 205 lowers the detection sensitivity for aline-like defect in the edge region. Specifically, in a case where thelocal pattern as the processing target is a high-contrast edge, then inthe region Ae_(H), the detection sensitivity adjustment unit 205 setsthe detection sensitivity for a line-like defect to be lower than thedetection sensitivity set for the inspection region A. In the regionBe_(H), the detection sensitivity adjustment unit 205 sets the detectionsensitivity for a line-like defect to he lower than the detectionsensitivity set for the inspection region B. In a case where the localpattern as the processing target is a low-contrast edge, then in theregion Ae_(L), the detection sensitivity adjustment unit 205 sets thedetection sensitivity for a line-like defect to be lower than thedetection sensitivity set for the inspection region A. In the regionBe_(L), the detection sensitivity adjustment unit 205 sets the detectionsensitivity for a line-like defect to be lower than the detectionsensitivity set for the inspection region B. FIG. 16B illustratesexamples of the adjusted detection sensitivities.

According to the present disclosure, it is possible to improve theaccuracy of inspection of the vicinity of a region including a featurein an inspection target image.

Other Embodiments

Embodiment(s) of the present invention can also be realized by acomputer of a system or apparatus that reads out and executes computerexecutable instructions (e.g., one or more programs) recorded on astorage medium (which may also be referred to mote fully as a‘non-transitory computer-readable storage medium’) to perform thefunctions of one or more of the above-described embodiment(s) and/orthat includes one or more circuits (e.g., application specificintegrated circuit (ASIC)) for performing the functions of one or moreof the above-described embodiment(s), and by a method performed by thecomputer of the system or apparatus by, for example, reading out andexecuting the computer executable instructions from the storage mediumto perform the functions of one or more of the above-describedembodiment(s) and/or controlling the one or more circuits to perform thefunctions of one or more of the above-described embodiment(s). Thecomputer may comprise one or more processors (e.g., central processingunit (CPU), micro processing unit (MPU)) and may include a network ofseparate computers or separate processors to read out and execute thecomputer executable instructions. The computer executable instructionsmay be provided to the computer, for example, from a network or thestorage medium. The storage medium may include, for example, one or moreof a hard disk, a random-access memory (RAM), a read only memory (ROM),a storage of distributed computing systems, an optical disk (such as acompact disc (CD), digital versatile disc (DVD), or Blu-ray Disc (BD)™)a flash memory device, a memory card, and the like.

While the present invention has been described with reference toexemplary embodiments, it is to be understood that the invention is notlimited to the disclosed exemplary embodiments. The scope of thefollowing claims is to be accorded the broadest interpretation so as toencompass all such modifications and equivalent structures andfunctions.

This application claims the benefit of Japanese Patent Application No.2020-058462, filed Mar. 27, 2020 which is hereby incorporated byreference herein in its entirety.

What is claimed is:
 1. An image processing apparatus comprising: a firstsetting unit configured to set a detection sensitivity such that thedetection sensitivity for a defect corresponding to a predeterminedlocal pattern in a reference image, which is a reference printingresult, is lower than for a region other than the predetermined localpattern in the reference image; an acquisition unit configured toacquire image data representing an image of an inspection target; and aprocessing unit configured to inspect the image of the inspection targetbased on the reference image and the set detection sensitivity.
 2. Theimage processing apparatus according to claim 1, wherein the localpattern includes a line-like pattern, and wherein the first setting unitsets the detection sensitivity such that a detection sensitivity for aline-like defect in a region corresponding to the line-like pattern inthe reference image is lower than for a region other than the line-likepattern in the reference image.
 3. The image processing apparatusaccording to claim 1, wherein the local pattern includes a point-likepattern, and wherein the first setting unit sets the detectionsensitivity such that a detection sensitivity for a point-like defect ina region corresponding to the point-like pattern in the reference imageis lower than for a region other than the point-like pattern in thereference image.
 4. The image processing apparatus according to claim 1,wherein the local pattern includes a line-like pattern and a point-likepattern, and wherein the first setting unit sets the detectionsensitivity such that detection sensitivities for a line-like defect anda point-like defect in regions corresponding to the line-like patternand the point-like pattern in the reference image are lower than for aregion other than line-like pattern and the point-like pattern in thereference image,
 5. The image processing apparatus according to claim 1,wherein the processing unit generates a difference image between thereference image and the image of the inspection target, enhances thelocal pattern on the difference image in a region corresponding to thelocal pattern, and detects the defect corresponding to the enhancedlocal pattern,
 6. The image processing apparatus according to claim 1,wherein the local pattern includes a plurality of local patternsdifferent from each other in contrast with a background in the referenceimage, and wherein the first setting unit sets the detection sensitivityso that the higher the contrast is with the background, the lower thedetection sensitivity is for the defect.
 7. The image processingapparatus according to claim 1, further comprising a second setting unitconfigured to set detection sensitivities for a plurality of types ofdefects in advance, wherein the first setting unit sets the detectionsensitivity by individually adjusting the detection sensitivities set bythe second setting unit.
 8. The image processing apparatus according toclaim 7, further comprising a third setting unit configured to set aplurality of inspection regions in the reference image, wherein thesecond setting unit sets the detection sensitivities for the respectiveinspection regions.
 9. An image processing method comprising: setting adetection sensitivity such that the detection sensitivity for a defectcorresponding to a predetermined local pattern in a reference image,which is a reference printing result, is lower than for a region otherthan the predetermined local pattern in the reference image; acquiringimage data representing an image of an inspection target; and inspectingthe image of the inspection target based on the reference image and theset detection sensitivity.
 10. A non-transitory computer-readablestorage medium storing instructions that, when executed by a computer,cause the computer to perform a method comprising: setting a detectionsensitivity such that the detection sensitivity for a defectcorresponding to a predetermined local pattern in a reference image,which is a reference printing result, is lower than for a region otherthan the predetermined local pattern in the reference image; acquiringimage data representing an image of an inspection target; and inspectingthe image of the inspection target based on the reference age and theset detection sensitivity.